The present invention relates to a mechanism for preventing a collision between a half-speed mirror and a zoom lens system in a variable scale factor copying apparatus.
FIG. 1 illustrates a variable scale factor copying apparatus which has been proposed by the applicant of the present application. In the variable scale factor copying apparatus of FIG. 1, a light source 4 reciprocates between a stand-by position A and a termination position B to radiate light for scanning an original document 3 which is mounted on a contact glass plate 2 that is disposed in front of a copying apparatus body 1. The image-carrying light reflected from the original document 3 is received by a full-speed mirror 5 which is moved along with the light source 4. The image-carrying light is reflected by half-speed mirrors 6 and 7 to a zoom lens system 8, and the zoom lens system is moved along its optical axis in accordance with a designated copying scale factor. The zoom lens system 8 emits the received, image-carrying light with the designated copying scale factor. The image-carrying light which is emitted from the zoom lens system 8 is radiated onto a photo-sensitive drum 10 through a fixed mirror 9 so that it forms an electrostatic, latent image of the original document, which is multiplied by the designated scale factor on the surface of the drum 10. Then, the copying operation is completed through ordinary steps.
In the steps mentioned above, it is necessary to move the half-speed mirrors 6 and 7 so that they can reduce the amount that is scanned by the full-speed mirror 5 by half to maintain the distance between respective images on the original document 3 and the sensitive drum 10 constant. In addition, an operator is required to move the zoom lens system 8 in accordance with the designated copying scale factor. Various scanning ranges of the half-speed mirror for several designated copying scale factor positions of the zoom lens system 8 are illustrated in FIG. 2. In order to reduce the size of the copying apparatus body, it is preferable to have the scanning zone of the half-speed mirrors 6 and 7 overlap the travelling zone of the zoom lens system 8. That is, the position of the zoom lens system 8 when the image of the original document is enlarged may enter the scanning end region of the half-speed mirrors 6 and 7 when the original document image is copied with an even or reduced scale factor.
Thus, since the zoom lens system 8 enters the scanning zone of the half-speed mirrors when the document image is enlarged, it is necessary to control the movement of the half-speed mirrors 6 and 7 so that these mirrors do not collide with the zoom lens system 8. However, the half-speed mirrors 6 and 7 are arranged so that they may scan the entire scanning range, and, therefore, there is a risk of a collision between the half-speed mirrors 6 and 7 and the zoom lens system 8 if the control system malfunctions and allows the half-speed mirrors 6 and 7 to move beyond the required amount.